This document describes a case study conducted by Pratt & Whitney Rocketdyne to qualify a replacement for a cadmium-bearing braze alloy currently used in manual brazing of the RL-10 rocket engine. Tests were conducted on the current alloy and two alternative cadmium-free alloys to evaluate their braze quality, shear strength, and cost. Both the current alloy and one alternative alloy performed similarly under testing, with uniform braze coverage and meeting the required minimum strength. However, the second alternative alloy did not flow as well due to its higher brazing temperature range requiring changes to the current process. In conclusion, one of the alternative alloys shows potential as an effective cadmium-free replacement for the

1. Eliminating Cadmium from the Production Process:
A Case Study
Alexander Rivas
Pratt & Whitney Rocketdyne
West Palm Beach, FL
Abstract
Cadmium is currently found in many production braze alloys because of its high strength, low
melting point, high corrosive resistance, and easy availability; but in brazing with cadmium comes a high
price of unsafe working conditions. Inhalation to the toxic cadmium can result in respiratory complications
and kidney failure. This is why OSHA has set a Daily Exposure Limit of cadmium to 5µg/m3
. Currently, at
the Pratt & Whitney Rocketdyne site in West Palm Beach, FL; cadmium is found in a manual touch-up
braze alloy for use on the RL-10 rocket engine. This case study hopes to initially qualify a replacement for
this cadmium-bearing alloy with a cadmium-free alloy. The research, setup, results, and conclusions for the
case study will explained in detail.
Introduction
The current cadmium-bearing alloy is used in touch-up oxygen
acetylene manual silver brazing on the RL-10 rocket engine. The chamber of
the RL10 is wrapped with thin-walled tubing that is used to transport cool
hydrogen gas which cools the engine during ignition. The thin tubing is
stainless steel base metal which is coating in a nickel-based bath. Then the
tubing is assembled around the RL10 and a reinforcing ring is furnace braze to
add support. The touch-up braze is used to braze any open gaps between the
thin tubing and between the thin tubing and the ring. Currently, the operator
must use an air purifier system the pulls in the excess dust and gas from the
alloy during brazing.
In establishing possible alloy alternatives, the following characteristics
were considered: melting temperature compatible with the base metal, good
wettability, high fluidity, adequate strength, and negligible physical/chemical interactions with base metal.
The baseline for comparison will be the current braze alloy (which is BRAZE 505 with AMS spec 4770).
This alloy is supplied by Lucas-Milhaupt, Inc. In searching for alternatives, these characteristics were
considered with more weight given to adequate strength and compatible melting temperature. The alloys
selected as possible alternatives were: BRAZE 560, BRAZE 505, BRAZE 450, BRAZE 452, and BRAZE
380 (all from Lucas-Milhaupt, Inc.). After further research into the brazing temperature range and density,
the two selected alloys to be tested were BRAZE 560 and BRAZE 505. These alloys had a similar braze
Figure 1 – Manual
braze location on
RL10
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2. temperature range, density; and the cadmium was replaced by a compatible alloy such as tin or nickel.
Table 1 shows the physical properties of the 3 alloys to be tested.
Table 1 – Physical characteristics of the three alloys in test.
Table 2 shows the nominal chemical compositions of the three alloys in comparison. Note that the
cadmium is nonexistent in the alternatives and is replaced by a new element. The original remaining
elements are still found in similar percentages.
Table 2 – Chemical compositions of the three alloys in test.
Pratt & Whitney is working towards creating and sustaining the safest, hazard-free working
environment. The EH&S (Employee, Health, and Safety) guidelines work to “Drive pollutants in
manufacturing processes to the lowest achievable levels.” Currently working with the cadmium-containing
alloy is not the lowest achievable level of pollutants. Eliminating the cadmium would eliminate all the
listed pollutants in the process and fulfill this EH&S guideline. The EH&S policy also aims to “Establish
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3. safety and environmental protection standards that comply with the applicable laws and company policies
and go beyond, when necessary, to achieve our goals.” This guideline refers to eliminating the cadmium
count beyond the minimum DEL. Cadmium is a proven pollutant and eliminating would go beyond the
baseline regulations and create a safer working environment.
The last component in comparison was cost. Even though cost is not a primary factor in the alloy
selection, it can still hold a strong influence if the cost is too high or very low.
Test Setup
The main objective to validate an alternative alloy was through a shear test. This test would
validate the required strength needed. Along the braze process, observations would be made regarding the
ease of brazing with the alternatives and their flow properties.
The test pieces were constricted to be plug brazed. The test pieces were made from 347 stainless
steel bar stock. A 1 inch male and 1 inch female were machined, coated in a nickel-based bath, heat treated
in furnace, brazed, and then threaded and bored. This process for the test pieces was set to mimic the
chamber tubing process, so to create a case study as representative as possible. A pictorial process map is
shown in Figure 2. The only difference in the process occurred with the braze alloys. 20 total pairs were
machined with 5 pieces dedicated to a furnace braze, 5 pieces for the current alloy AMS 4770, 5 pieces for
the alternative alloy AMS 4763, and 5 pieces for the alternative alloy AMS 4788.
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Figure 2 – Process Cycle of test pieces.

4. The blueprint of the test pieces is available in the Appendix at the end of this paper. This blueprint
gives the dimensions and clearances used. The pieces were heat treated in an oven with 1000-1500 microns
in pressure and max temperature of 1875-1900o
F. All the manual braze were wired brazes with an oxygen-
acetylene torch. The braze alloys were cleaned before use to eliminate any impurities. The threading was
used to securely load and hold the pieces during the pull shear test. Lastly, the excess braze was bored out
to create a standard braze area among all the test pieces. After all test pieces were prepared, they were sent
to the materials lab for tests.
Lab Results
One pair from each alloy was sliced in half and examined under the microscope. The remaining
test pieces were shear tested. Two pairs of each alloy were pulled in room temperature and two pairs were
pulled at -320F. These conditions were chosen to mimic the nominal conditions of the RL10 at the launch
pad and in space.
The braze area pictures from the microscope show the alloy’s flow across the surface of the two
pieces. A smooth, uniform flow with minimal gaps is ideal and result from good fluidity and correct
brazing. A uniform braze area will also correctly result in a highly representative shear strength when the
piece is pulled. Figure 3 shows the pictures of the brazed alloys at 100x magnification. Note that all alloys
show uniform braze lines except for the alternative alloy AMS 4788. This may be due to its higher brazing
temperature range and will be explained in further detail in the Conclusions section.
Manual Braze 1
(AMS 4770)
Furnace Braze
Manual Braze 2
(AMS 4763)
Manual Braze 3
(AMS 4788)
Figure 3 – Braze Areas under 100 x magnifications
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5. The shear test was then used
to measure the strength of each braze
alloy. The pieces were pulled until the
alloy fractured and the pieces were
separated. The force at which the
fracture occurred was recorded as the
maximum shear strength. Figures 4 and
5 show the Load versus Deflection of
the pieces pulled at room temperature
and -320F, respectively. The highest
point of the curve shows the maximum shear strength. Note that for the -320F test, alternative alloy AMS
4788 had a strength higher than the range of the test, so the last maximum value was used. Table 3 lists the
abbreviations that were used to label each piece.
Table 3 – Piece Labels
20050012 Barrel Braze RT
0
2000
4000
6000
8000
10000
12000
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Deflection (in)
Load(lbs)
FB1
FB1
HB1 4770
HB1 4770
HB2 4763
HB2 4763
HB3 4788
HB3 4788
Figure 4 – Shear tests at room temperature.
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6. 20050012 Barrel Braze LN2 -320F
0
2000
4000
6000
8000
10000
12000
14000
16000
0 0.02 0.04 0.06 0.08
Deflection (in)
Load(lbs)
0.1 0.12
FB1
FB1
HB1 4770
HB1 4770
HB2 4763
HB2 4763
HB3 4788
HB3 4788
Figure 5 – Shear tests at -320F
After the pieces were pulled and the maximum strength was recorded, the braze areas were
measured to note for any outliers or discrepancies. Each piece was examined under a magnification glass
and braze coverage area estimates on each piece were recorded. If the piece had full braze coverage, then
the shear test correctly represented the strength of the alloy. If the braze coverage was weak and not
uniform, then the measured strength was not fully representative. Figure 6 shows examples of braze area
coverage. On a low percentage braze area piece, the potential strength may be higher than the measured
strength if the braze area were 100%. Therefore, each piece was measured for the braze area which was
used with the measured strength to estimate the potential strength. Table 4 shows these results.
Female Piece example Male Piece example
Figure 6 – Braze Area Visual Measurements
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7. Table 4 – Maximum Load, Measured Braze Area, and Estimated Potential Load
Conclusions
The primary purpose of the case study was to prove that cadmium-free alloys can effectively
replace the current alloy. In certifying this replacement, the braze alloy should hold the needed minimum
strength. The alloy should also achieve good flow under the same brazing temperatures so to achieve
maximum strength without changing the current operating procedures. The last comparison was the price,
which will determine if a replacement is financially possible.
When looking at the braze coverage, the current braze alloy and the alternative braze alloy AMS
4763 displayed good flow. Most pieces were above 90% braze coverage, so the shear test was highly
representative of the alloy’s strength. Alternative alloy AMS 4788 showed the least braze coverage area
and this can be explained by its higher braze temperature range. All hand brazes were performed in the
range of the current hand braze (1160-1175F) and the temperature range for AMS 4788 was 1220-1305F.
So to achieve a greater braze coverage with the alternative alloy AMS 4788, a higher torch temperature (or
longer duration) should be used during brazing.
Then, taking consideration of the braze coverage, the strengths were compared. Using the current
braze alloy as the baseline, the two alternative alloys displayed equal (and in some cases greater) strengths.
The alternative alloy AMS 4763 performed most closely to the current alloy in the room temperature, but
performed slightly lower in cryogenic temperature. The alternative alloy AMS 4788 showed the greatest
strengths in both conditions (with the exception of one piece), even though it displayed the poorest braze
coverage.
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8. Therefore, the AMS 4788 alloy displayed the highest strength out of the three in test, but requires
a higher braze temperature for good flow. The alternative alloy AMS 4763 performed similar to the current
alloy AMS 4770 and can be brazed at the same temperature currently used.
Finally, in comparing the prices, the alternative alloys both offer a savings from the current alloy.
Table 5 shows the projected costs of the three alloys in comparison. Notice that the cost for both alloys is
less than the current allow and would result in significant savings over a yearly supply. The costs were
based on a silver metal market of $8.600 per troy oz and the yearly supply was based on an order of 120 of
‘-2S’ rods and 110 of ‘-3S’ rods. Note that the all the braze alloys were supplied and quoted from Lucas-
Milhaupt, Inc.
Table 5 – Cost comparison between three alloys in comparison.
Recommendations
This case study is meant to set a starting point in the process to certify a cadmium-free braze alloy
for use in production. The results show that an alternative that holds the same (or better) strength, requires
similar braze processing, and does not add cost is possible. If more tests and pieces are needed to validate a
new alloy, the author recommends more pieces are run. In brazing the alternative alloy AMS 4788, a higher
braze temperature should be used to achieve good flow and near 100% braze coverage.
Acknowledgements
The author would like to thank Russell Melnick for initiating and mentoring this case study. The
author is largely grateful to Mike Gehron for treating this study as his own and all the work he put into it.
The author would like to also thank the Pratt & Whitney Rocketdyne team in West Palm Beach, FL for all
their support, guidance, and assistance; especially to the Combustion Devices Operations Center, machine
shop operators, and materials laboratory. Lastly, many thanks to Andy Turko from Pratt & Whitney in East
Hartford, CT for his helpful insight and advice.
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9. Appendix
Test Piece Specimen Blueprint:
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